Microwave transmission lines



J1me 1957- J. A. KOSTRIZA ErAL I MICROWAVE TRANSMISSION LINES Filed Jan. 9. 1953 l3 l2 l4 15 F 2,0 22 21/ F 7-' J FIG. 4

INVENTORS JOHN A. KOSTR/ZA PAUL TERRANOVA ATTORNEY MICROWAVE TRANSMISSION LINES John A. Kostriza, New Dorp, and Paul Terranova, Brooklyn, N. Y., assignors to International Telephone and Telegraph Corporation, a corporation of Maryland Application .lanuary 9, 1953, Serial No. 330M270 14 Claims. (Cl. 333--9) This invention relates to microwave transmission lines and more particularly to networks of such lines including bends and energy dividing junctions.

In the copending applications of D. D. Grieg and H. F. Engelmann, Serial No. 234,503, filed June 30, 1951, now Patent No. 2,721,312, H. F. Engelmann, Serial No. 237,857, filed July 21, 1951, now Patent No. 2,654,842 and M. Arditi and P. Parzen, Serial No. 286,- 764, filed May 8, 1952, now Patent No. 2,774,046, microwave transmission lines comprising generally a line- :above-ground type of transmission line, over which microwave energy may be propagated in a mode simulating a TEM mode, are shown. In this type of transmission line, a planar conductor is employed as a ground conductor with a line conductor disposed in spaced parallel relation thereto by means of a strip or layer of dielectric material. The line and planar conductors are preferably of different widths, that is, the planar conductor is made wider than the line conductor so that it appears as a infinite conducting surface to the line conductor, thereby insuring an electric field distribution characterized generally by the TEM mode. For example, the field distribution is believed to be similar to that which occurs between one of the conductors of a truly parallel conductor system and the neutral plane between such conductors. The important parameters of this type of transmission line are the width of the line conductor and the dielectric spacing between the line conductor and the planar conductor.

One of the objects of this invention is to provide a microwave transmission line of the character described above with angular bends and/or energy dividing junctions without undue loss by radiation.

Another object of the invention is to provide such lines with angular bends between 30 and 90 without undue loss by radiation.

Still another object is to provide a network of such lines for power dividers, the network including angular bends at the power dividing junction thereof.

One of the features of this invention is the provision at the angular bends of means for tuning out the elfects of the discontinuity presented by the bend. This is accomplished by extending the line conductor axially thereof beyond the bend to form a tuning stub which may be provided with suseeptance means suitably spaced fromthe stub junction at the bend to tune out the effects of higher order modes caused by the angular change in the path of microwaves propagated along the line. Such principle is also employed where a network of such transmission lines are employed as an energy divider, one of the lines being extended beyond the junction thereof as a tuning stub. Impedance matching 2,797,390 Patented June 25, 1957 nice is also further enhanced in the network by the provision of suitable transformer shapes in the line feeding branch lines of the network.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a plan view of a microwave transmission line of the line-above-ground type incorporating an angular bend in accordance with the principles of this invention;

Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1;

Figure 3 is a plan view similar to Figure 1, showing an angular bend in which the tuning stubs are predetermined so that they may be formed during a circuit printing process; and

Figure 4 is a plan view of a network of such transmission lines in the form'of an energy divider.

Referring to Figures 1 and 2, the transmission line comprises a first or planar conductor 1, a second or line conductor 2 spaced apart by a thin strip or layer of dielectric material 3. The two conductors l and 2 are preferably of flat strip form, the planar conductor being wider than the line conductor so that propagation of microwave energy therealong is similar to the TEM mode as hereinbefore explained. The dielectric material may be of polystyrene, polyethylene, polytetnafluoroethylene (Teflon), Fiberglas or laminated Fiberglas impregnated with Teflon, quartz, or other suitable material of high dielectric quality. The conductors 1 and 2 may be formed on the dielectric strip by any of the known printed circuit techniques, one suitable method being an electrolytic etching process.

The transmission line shown in Figure 1 comprises a first section 4 and a second section 5 disposed at an angle to each other to form a right angle or L shaped bend. The planar conductors 1 of the two sections are connected together as an integral continuous planar strip conductor of right angle configuration. The line conductors 2 of the two sections intersect and as shown extend beyond the connection 6 to form two stubs 7 and 8 which overlie the surface of the planar conductor 1.

In making plain angular bends of the line conductor 2 of this type of transmission line it has been found that loss due to radiation is negligible for angular bends or up to approximately 30. As the angle becomes greater than 30 the loss due to radiation increases and becomes an important factor and therefore must be minimized. The reason for this loss is believed to be the establishment of higher order modes due to the discontinuity provided by the angular bend in the transmission line. The stubs 7 and 8 may be so proportioned and provided with susceptances as to tune out the elfects of the higher order modes established by the angular bend. As shown in Figures 1 and 2, by the positioning of a conductor 9 diagonally across the two stubs and adjusting the position thereof relative to the junction 6, these higher order modes can be substantially entirely tuned out. In the place of a single conductor 9 each stub may be provided with an individual'susceptance conductor disposed crosswise thereof and adjusted the proper distance from the junction 6 to provide requisite tuning.

In Figure 3 the same type of angular bend is shown as illustrated in Fig. lwith the exception thatthe stubs 7g and 8:: thereof are provided with independent susceptance elements in the form of lateral extensions of the lines as indicated at 10 and 11. These integral extensions may be predetermined by adjusting a strip of conductor along the stub to determine the desired size and location after which it may be formed as a part of the line conductor by the printing process employed in making the line conductor.

By way of example, an angular L bend such as illus trated on Fig. 3 was constructed for 4700 mcs./sec., the dimensions being as follows:

a==0.22 inch b=0.34 inch c=0.9 inch d=0.55 inch Thickness of dielectric (polystyrene) was inch Width of planar strip conductor 1 was 2.25 inches The L bend with the foregoing dimensions gave the following characteristics in the band 4400 to 5000 megacycles per second:

Frequency mcs./sec.: V. S. W. R. 4400 1.32 4450 1.31 4500 1.30 4550 1.29

It will be noted from the foregoing table that substantially no loss due to radiation occurred at 4700 megacycles per second for which the band was designed. Where the printed tuning stubs do not give satisfactory tuning for a particular frequency the tuning may be changed by slicing away or adding to the susceptance sections 10 and 11.

Referring to Figure 4, the network there shown comprises a power divider wherein section 12 comprises the main line over which microwave energy is propagated, as indicated by the arrow 13. The energy is divided over branch lines 14 and 15 as indicated by arrows 16 and 17. The junction of the line conductors of the three sections at 17a tend to establish higher order modes similarly as the case of the L bends of Figures 1 and 3. These higher order modes, however, are tuned out by stub 18 which forms an extension of the line conductor 19 of section 12. Since the line conductor 19 is coupled to the line conductors 20 and 21 of the two branches 14 and 15 there is also a problem of impedance matching and this is accomplished by a transformer section 22 printed as an integral part of the conductor 19 adjacent the junction 17. This transformer configuration may take various forms so as to provide a proper transition between the impedance of the single line 19 and the two lines 20 and 21. The particular transformer section 22 shown comprises a pie shaped sector. The radius of this sector may be varied for difierent line widths and dielectric spacing. In an example which gave favorable results for 4700 mcs./sec., the radius of the pie sector 22 was selected of an inch, the apex of which was located of an inch from the center line of the conductors 20, 21, and the angle a was 90. The dimensions of the'line conductors and stub were the same as those given for Figure 3. The specimen of this example was tested over a band of 4400 to 5000 megacycles per second, werein substantially equal power division was obtained over the two branches 14 and 15. The following table gives the voltage standing wave ratio for the corresponding frequencies indicated.

When optimum results are desired for a frequency different from 4700 mcs./sec., the dimensions of the stub 18 and transformer 22 require change, and for higher frequencies the corners of sector 22 should be rounded. The size of the sector may also be varied for different positions relative the center line of branch lines 20, 21.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. A microwave transmission line having two sections with the longitudinal axes thereof disposed at a substantial angle to each other, each section comprising a first conductor, a second conductor and means to maintain said conductors in spaced substantially parallel relation, each of the conductors being of flat strip configuration and said second conductor being narrower than said first conductor so that the latter presents substantially a planar surface with respect to said second conductor, the space between said first and second conductors being conductively open along the lateral edges of said conductors and therefore subject to radiation losses due to discontinuities such as sharp bends in said lines, the first conductors of said two sections being connected together as a continuous planer conductor, the second conductors of said sections being connected together and at least one of said second conductors having a part extending axially thereof beyond the connection to form a stub and in overlying relation to the planar surface of said first conductors, and susceptance means carried by said stub to counter substantially the radiation effects produced by the angular connection of said sections.

2. A microwave transmission line according to claim 1, wherein the angular bend between said sections is selected between 30 and 3. A microwave transmission line according to claim 1, wherein the susceptance means comprises a third conductor of fiat configuration disposed crosswise of said stub, and in overlying parallel relation to the planar surface of said first conductors.

4. A microwave transmission line according to claim 3, wherein said third conductor includes laterally disposed portions integrally connected to the second conductor of said stub.

5. A microwave transmission line according to claim 1, wherein each of the second conductors of said sections has an extension in the form of a stub beyond said connection.

6. A microwave transmission line according to claim 5, wherein the susceptance means comprises a third conductor adjustable in position diagonally across said stubs.

7. A microwave transmission line according to claim 5, wherein each of the said stubs is provided with susceptance means in the form of lateral integral extensions of the second conductor thereof.

8. A microwave transmission line according to claim 1, wherein one of the sections is extended beyond said connection thus forming two branches with respect to the other of said sections whereby energy propagated along said other section divides between said two branches.

9. A microwave transmission line according to claim 8, wherein the second conductor of said other section has an impedance transformer portion located adjacent said connection, said impedance transformer portion being larger in width than said second conductor and in spaced parallel relation to said first conductor.

10. A microwave transmission line according to claim 9, wherein said impedance transformer portion comprises a pie-shaped sector with the apex thereof located closely adjacent the center of said connection.

11. A microwave transmission line having an L bend therein comprising a first conductor, a second conductor, a layer of dielectric material separating said first and second conductors in spaced substantially parallel relation, said conductors being of fiat strip configuration with the second conductor being narrower than said first conductor so that the adjacent surface of said first conductor appears as a planar surface to said second conductor, the space between said first and second conductors being conductively open along the lateral edges of said conductors and therefore subject to radiation losses due to discontinuities such as sharp bends in said lines a pair of stub conductors, one each disposed in alignment with one of the legs of said second conductor at said bend, said stubs overlying in spaced substantially parallel relation said first conductor, and a third conductor disposed substantially diagonally across said stubs as a tuning susceptance for each of said stubs, to counter substantially the radiation effects produced by said bend.

12. A microwave transmission line having an L bend therein comprising a first conductor, a second conductor, a layer of dielectric material separating said first and second conductors in spaced substantially parallel relation, said conductors being of fiat strip configuration with the second conductor being narrower than said first conductor so that the adjacent surface of said first conductor appears as a planar surface to said second conductor, the space between said first and second conductors being conductively open along the lateral edges of said conductors and therefore subject to radiation losses due to discontinuities such as sharp bends in said lines, a pair of stub conductors, one each disposed in alignment with one of the legs of said second conductor at said bend, said stubs overlying in spaced substantially parallel relation said first conductor, each of said stubs being provided with a lateral extension of the second conductor thereof to form a susceptance spaced a predetermined distance from said connection to counter substantially the radiation eifects produced by said bend.

13. A microwave transmission network comprising a main section and a pair of branch sections, said main section being disposed at right angles to said branch sections for division of energy propagated along said main section, each of said sections comprising a first conductor, a second conductor and a thin layer of dielectric material spacing the first and second conductors thereof in substantially parallel relation, the space between said first and second conductors being conductively open along the lateral edges of said conductors and there fore subject to radiation losses due to discontinuities such as sharp bends in said lines the second conductor being narrower than said first conductor so that the adjacent surface of said first conductor appears as a planar surface to said second conductor, the second conductor of said main section having an impedance transformer portion adjacent the connection thereof to the second son ductor of said branch sections, and a stub tuner comprising an extension of the second conductor of said main branch beyond said connection but in overlying parallel relation to said first conductor, to counter substantially the radiation effects produced by the angular connection of said sections.

14. A microwave transmission network according to claim 13, wherein said impedance transformer section comprises a pie-shaped sector With the apex thereof located adjacent the center of said connection.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,553 Ramo Nov. 26, 1946 2,411,555 Rogers Nov. 26, 1946 2,446,982 Pound Aug. 10, 1948 2,602,856 Rumsey July 8, 1952 2,611,822 Bliss Sept. 23, 1952 2,654,842 Engelmann Oct. 6, 1953 2,721,312 Grieg et al. Oct. 18, 1955 

